```typescript
function parseSemver(version: string): { major: number; minor: number; patch: number; prerelease: string | null; build: string | null } {
  const re = /^v(\d+)\.(\d+)\.(\d+)(?:-([^0-9-.]+|-alpha-num-\d.*)?)?(?:\+(beta|delta)-?(\w+)\+(\w+\.\w+\.\d+))?$/;
  const match = re.exec(version);

  if (!match) {
    throw new Error(`invalid semver format: ${version}`);
  }

  return {
    major: parseInt(match[1], 10),
    minor: parseInt(match[2], 10),
    patch: parseInt(match[3], 10), // assuming the prerelease+build version format is used for digit-only strings
    prerelease: match[4] ? match[4].trimStart('-') : null, // trimming leading '-' if present
    build: match[6] ? `${match[6]}+${match[7]}/${match[8]}` : match[5] ? match[5].trimStart('-') + '+' : null // parsing build from prerelease string or full build string otherwise
  };
}
```